This invention pertains to push-pull cable-type actuators of the class used as remote control devices. It pertains particularly to push-pull type remote control devices which may be used over long distances in tortuous runs and which may include either a sliding or a ball bearing-mounted power transmission element of simplified construction.
Although there are many types of push-pull cable actuators known to the prior art, there is needed for an actuator of this class which is adaptable for the transmission of high loads without the occurrence of backlash or other mechanical problems. There also is need for a low friction ball bearing-type push-pull cable control of simplified construction which is flexible in all planes.
A typical prior art bearing type push-pull cable control is characterized by the presence of tracks laid inside a tightly wound coiled wire flexible sheath. The tracks provide a smooth surface on which the ball bearings roll. They are undesirable because of their added cost, the difficulty in adjusting the control to different planes of bending, and the need for complicated fittings to secure the ends of the sheath.
Stated in greater detail, the presence of the tracks causes difficulties when bending the conduit because as the bend plane of the conduit is changed, the tracks must move circumferentially within the sheath to allow the motion transmission core member to align with the bent plane. Also, the tracks must be secured at their ends to transmit axial load to the sheath. Since bending creates a differential length between the two tracks, the extent of bending of the sheath is restricted correspondingly. Still further, the securing means for the tracks creates a gap in the ball bearings at the full extension of the motion transmission core member. This in turn reduces the compression capability of the core member.
As a substitute for the tracks of the above described ball bearing type control the use of a plastic sheath has been suggested. The use of such a sheath provides a smooth surface for the operation of the ball bearings, and allows unlimited flexing. However, the low bearing stress capability of plastics severely limits the allowable load that may be transmitted by such a control.
The use of a metal tube as the sheath will overcome the latter problem and permit high loads to be transmitted. However, a metal sheath is not sufficiently flexible to allow easy installation and efficient operation.
It is the general purpose of the present invention to provide a push-pull, cable-type actuator which overcomes the foregoing problems and which permits the efficient use of a ball bearing-mounted central core, or power transmission member, while retaining a high degree of actuator flexibility and strength.
It is another object of the present invention to provide a push-pull, cable-type actuator which is universally applicable for use with both ball bearing type and sliding type core members, or with combinations of both.
Another important object of the present invention is the provision of a ball bearing type push-pull actuator which is of simplified construction and which accordingly is of relatively low cost.
Still a further object of the present invention is the provision of a push-pull cable-type actuator which may be used to transmit high loads over great distances; which is universally applicable too both straight line and devious courses of application; and which is free from backlash and other operating difficulties.